The role of the external ear in temporary threshold shift (TTS) has been studied quantitatively in 13 normal hearing human adult subjects. The experiment investigated the relationship between the amount of acoustic pressure gained at the eardrum provided by the external ear and resulting TTS. The premise is that changes in magnitude of TTS can be predicted by known changes in sound pressure level impinging upon the eardrum. Based upon TTS measures made when the fatiguing stimulus was adjusted in the sound field and measures of outer ear pressure gain, it was shown that the mean magnitude of TTS was within 1 dB of what was predicted when the fatiguer was adjusted at the eardrum. The standard deviations between the treatment levels were not significantly different. The data accrued to date indicated the absence of a significant difference in the study groups.